EP1333781B1 - Joint prosthesis - Google Patents

Abstract

In a joint prosthesis the head cap is connected via a collar piece to the shaft piece which may be anchored in the bone. The collar piece is coupled to the shaft piece by a joint head in a ball-jointed manner. The articulation surfaces between the joint cavity in the shaft piece and the articulation head on the collar piece are embodied such that on pressing the articulation head to the base of the joint cavity, edges or projections on the one articulation surface digs into the other articulation surface lying on a virtual spherical surface. It is thus possible to achieve a ball-joint like articulation, whereby the spherical surfaces may have a relatively large production tolerance without the above affecting the clamping connection between the articulation surfaces.

Description

Technical field of the invention

The invention relates to a joint prosthesis, in particular a humeral head prosthesis, according to the preamble of claim 1.

State of the art

A composite endoprosthesis with a metal shaft and a ceramic joint part is known from EP 0 024 442. The ceramic part has a conical or cylindrical recess. Supporting ribs are formed on a metallic pin of the metal shaft to be inserted into the recess. These support ribs are plastically and elastically deformed when the harder ceramic joint part is put on. An interference fit between the endoprosthesis parts is thereby achieved

A humeral head prosthesis is known from EP-A-0 712 617, in which a pivot ball connected to a spherical cap via a stem is articulated in a pit with a hollow spherical base on a shaft part. To fix the articulation ball in the pit, one or more grub screws are provided, which can be screwed through the shaft part against the articulation ball. In one exemplary embodiment, the c-shaped cut-open ball is pressed together with the grub screw in order to clamp the stem stuck in a central bore in the set ball. In another embodiment, a grub screw is provided, which can be screwed along the axis of the handle through the articulation ball and against the base of the pit. This screw is used to press the pivot ball against the opening of the pit through which the stem protrudes from the pit. In a further example, knobs on the pit base interacting with depressions in the ball surface are provided for indexing the position of the pivot ball.

From WO 99/34756, which corresponds to FR-A-2 773 469, a joint prosthesis according to the preamble of claim 1 is known, in which a neck part is pivoted therein in a hemispherical recess in the shaft part. The neck part has a hemispherical articulation surface and one against an axis through it Ball center eccentric conical surface for attaching a spherical cap. The neck part has a bore open from the calotte side with a hemispherical base. A screw with a spherical head, which is inserted into the bore and can be screwed through an opening in the base of the shaft part, acts on the base. The spherical surfaces of the hemispherical recess in the shaft part, the articulation surface on the shaft part, the bottom of the bore and the screw head must have the same center. The two interacting hollow and solid spherical surfaces must also be manufactured very precisely and have the same radius. Smallest deviations from the ideal dimensions lead to the fact that the neck part cannot be connected to the shaft part sufficiently firmly in order to reliably prevent unintentional pivoting of the neck part relative to the shaft part during use of the joint. The precision of the spherical surfaces required for this, however, proves to be very difficult to achieve.

DE-U-299 18 589 sets itself the task of avoiding precisely this disadvantage of interacting spherical surfaces. For this purpose, she proposes an endoprosthesis for a shoulder, in which a rotating piece is arranged in a shaft part, which can only be rotated about a first axis. A directional piece is pivoted on this rotating piece, which can be pivoted about only a second axis. The straightening piece extends along a neck axis, which - thanks to which the first and second axes cross - can be brought into any desired position and locked in it, similar to a ball joint.

DE-U-29918 589 thus teaches to avoid a ball joint and to simulate the ball joint movement by dividing it into two independent movements around two discrete axes. Thanks to the avoidance of spherical surfaces, the articulation and friction surfaces between the shaft part, rotating piece and straightening piece are surfaces of rotating bodies such as cylinders, torus and cones. These surfaces are easier to produce with sufficient precision.

To determine the pivoting movement of the straightening piece relative to the rotating piece, it is proposed that the interacting articulation surfaces advantageously only correspond in such a way that a line contact takes place between them. For this, the The articulation surface on the rotating piece can be designed as a channel with two flat surfaces at an angle to one another. A hole in the directional piece, against which the ball head of a screw presses, can also be conical. It is further suggested that the articulation surfaces can also have edges and domes that can be pressed into the counter surface when the screw is tightened. An example of this is not given.

Object of the invention

It is an object of the present invention, in a joint prosthesis with a shaft part that can be anchored in the bone and a neck part articulated thereon and a spherical cap arranged on the neck part, both the manufacturing tolerances for the articulation surfaces involved in the ball joint and the reliability of the immobilization of the ball joint compared to the stand of technology to increase.

Description of the invention

According to the invention, in a joint prosthesis according to the preamble of patent claim 1, a first of the two interacting articulation surfaces has at least one edge and / or tip. In addition, the articulation surfaces are designed in such a way that only one or more contact areas result between the edge and / or tip of the first articulation surface and the second articulation surface lying on a virtual spherical surface. Furthermore, the articulation surfaces are designed in such a way that at least the second articulation surface in the contact area can be plastically deformed by the edge and / or tip of the first articulation surface under the action of the compressive forces that occur during the pressing.

As a result, when the pressed part is pressed on, at least one edge or tip of one articulation surface is buried in the second articulation surface and toothing or clawing of the two articulation surfaces is achieved. The toothing allows the tolerances during production to be increased. In spite of the mismatched surface shape and despite the relatively large inaccuracies in the dimensions, a ball joint is created which can be reliably immobilized. A deformation of the material is necessary for pivoting or rotating the once-attached coupling head relative to the coupling trough and therefore very high forces are required. Nevertheless, the pivot head is in The articulation trough is guided and can be pivoted in a ball-and-socket joint as long as the pressed part is not firmly pressed, but only lies against it.

The joint prosthesis has a shaft part that can be anchored in the bone. This is matched to the bone in a known manner and is selected from a set of shaft parts at most. A neck part is articulated to the shaft part and defines a neck axis. The neck part is equipped to accommodate a head cap or part of the head cap. Furthermore, the joint prosthesis is also equipped with a head cap, which is designed for the joint socket interacting with the head cap. The head cap is shaped as close as possible to the removed natural cap and is therefore selected from a set of caps at most. The joint prosthesis also has at least one press part for pressing the neck part onto the shaft part and means for connecting the press part and shaft part. For the articulation of the neck part on the shaft part, a coupling trough is formed either on the neck part or on the shaft part and a coupling head to be arranged in the coupling trough is formed on the other part. The coupling head can be pivoted or rotated in the coupling trough at least about two mutually perpendicular axes. Depending on whether the socket is also replaced or not, the joint prosthesis also has an artificial socket that can be anchored in the bone. If the natural socket is preserved, the calotte works with it.

The plastic deformation of a contact area in the articulation trough or a contact area on the articulation surface of the articulation head not only means that the necessary precision of the parts can lie within conventional manufacturing tolerances and does not place increased demands on the production and the checking of the dimensional accuracy of the parts. The deformation of the articulation surface also leads to a non-pivoting connection between the shaft part and the neck part. In the deformed area, both or only one involved surface can be deformed when the articulation surfaces are pressed. If it is predominantly the neck part that experiences the deformation, this can be replaced, for example when the joint prosthesis is revised, without the shaft part having to be replaced.

If the contact areas between the base of the articulation trough and the articulation head have one or more point contacts, or also one or more continuous or interrupted line contacts, the amount of pressure exerted in these areas is inversely proportional to the size of the contact areas. As a result, stronger deformations can be achieved.

If one of the articulation surfaces is formed by one or more body edges or one or more body tips, and the other articulation surface is formed by a surface area, the body tips and body edges are pressed into the other articulation surface and deformed articulation surfaces are created, the alignment of which is transverse to a tangent to a circle stand around the swivel center. This results in a toothing between the neck part and the shaft part, and therefore a secure connection that also withstands relatively large forces on the ball joint between the base and the neck part. The surface area can be smooth or rough. The options range from smooth to untreated after machining to polished. A rough surface can be grooved or porous, it can be etched, blasted, cast or machined or otherwise structured. It is advantageous to take into account the fact that the two articulation surfaces remain practically continuously pivotable relative to one another. Rough surfaces are therefore more suitable for line contact and smooth surfaces for point contact.

In the exemplary embodiments, the contact area lies on a virtual spherical surface. This has the advantage that the ball-joint-like pivotability between the neck part and the shaft part is given without additional measures the jamming torques acting on the neck part. This prevents the neck part from rotating around the neck axis, which ensures that the selected position between the neck part and the shaft part is not changed during or after the two are pressed together. Conversely, the spherical surface area can also have grooves and edges. These are also advantageously transverse to the strongest torque acting on the neck part In addition to the small-area contact areas between the shaft part and the neck part, it is also advantageous to provide those between the neck part and the press part. There is therefore advantageously at least one continuous or interrupted line contact between the articulation head and the pressed part.

Brief description of the figures

Fig. 1

eine teilweise geschnittene Darstellung einer erfindungsgemässen Schultergelenkprothese mit kugelförmigem Anlenkkopf in einer Anlenkmulde mit einer Kreiskante als Anlenkfläche,

Fig. 2

eine teilweise Geschnittenen Darstellung einer Schultergelenkprothese ohne Kopfkalotte mit gegen einen kugelförmigen Grund der Anlenkmulde gerichteten Spitzen am Anlenkkopf des Halsteils,

Fig. 3

eine teilweise geschnittene Darstellung einer Schultergelenkprothese mit kugelförmigen Anlenkkopf und sowohl in den Anlenkkopf einpressbaren Kreiskanten als auch einer solchen Spitze im Grund der Anlenkmulde,

Fig. 4

eine teilweise geschnittene Darstellung des Kopfbereichs einer Schultergelenkprothese mit zylindrischem Anlenkkopf in kugeliger Anlenkmulde,

Fig. 5

eine teilweise geschnittene Darstellung des Kopfbereichs einer Schultergelenkprothese mit am Grund der Anlenkmulde ausgebildeten Kreiskanten in Berührung mit einer Kugeloberfläche am Anlenkkopf und einer unterbrochenen Kreislinie als Anlenkfläche zwischen auf einem Kreis liegenden Spitzen am Anlenkkopf und einer Kugeloberfläche am Pressteil,

Fig. 6

eine Schnittdarstellung durch den Kopfbereich einer Schulterprothese mit kugelförmigem Anlenkkopf und kegelförmig ausgebildetem Grund der Anlenkmulde,

Fig. 7

eine teilweise geschnittene Darstellung des Kopfbereiches einer Schulterprothese mit halbkugeligem Grund der Anlenkmulde und darin einem zu diesem Grund hin zylindrisch geformten Anlenkkopf, welcher zur Anpressscheibe mit einer Kreiskante als Anlenkfläche hin eine Kugeloberfläche aufweist,

Fig. 8

eine Schnittdarstellung durch den Kopfbereich einer Schulterprothese mit halbkugeliger Anlenkmulde und zylindrischem Anlenkkopf, bei welchem das Pressmittel eine Schraube durch das Zentrum des Anlenkkopfes ist,

Fig. 9 und 10

Ansichten von zwei Teilen, die zusammen ein Halsteil bilden,

Fig.11

eine Aufsicht auf das Halsteil aus den Teilen gemäss Figuren 9 und 10 mit Exzenterring

Fig. 12

eine teilweise geschnittene Darstellung einer Schultergelenkprothese mit einem Halsteil gemäss Figuren 9 bis 11 und einem Spannbügel.

The invention will now be explained on the basis of exemplary embodiments. It shows:

Fig. 1

3 shows a partially sectioned representation of a shoulder joint prosthesis according to the invention with a spherical articulation head in a articulation depression with a circular edge as articulation surface,

Fig. 2

3 shows a partially sectioned representation of a shoulder joint prosthesis without a spherical cap with tips directed against a spherical base of the articulation depression on the articulation head of the neck part,

Fig. 3

2 shows a partially sectioned representation of a shoulder joint prosthesis with a spherical articulation head and circular edges which can be pressed into the articulation head and such a tip in the base of the articulation depression,

Fig. 4

a partially sectioned representation of the head area of a shoulder joint prosthesis with a cylindrical articulation head in a spherical articulation depression,

Fig. 5

a partially sectioned representation of the head region of a shoulder joint prosthesis with circular edges formed at the base of the articulation depression in contact with a spherical surface on the articulation head and an interrupted circular line as articulation surface between tips lying on a circle on the articulation head and a spherical surface on the press part,

Fig. 6

2 shows a sectional view through the head region of a shoulder prosthesis with a spherical articulation head and a conical base of the articulation depression,

Fig. 7

3 shows a partially sectioned representation of the head region of a shoulder prosthesis with a hemispherical base of the articulation depression and therein an articulation head which is cylindrical in shape for this reason and which has a spherical surface toward the pressure disc with a circular edge as the articulation surface,

Fig. 8

2 shows a sectional view through the head region of a shoulder prosthesis with a hemispherical articulation depression and a cylindrical articulation head, in which the pressing means is a screw through the center of the articulation head,

9 and 10

Views of two parts that together form a neck part,

Figure 11

a top view of the neck part from the parts according to Figures 9 and 10 with eccentric ring

Fig. 12

a partially sectioned representation of a shoulder joint prosthesis with a neck part according to Figures 9 to 11 and a clamping bracket.

Description of the embodiments

For the sake of clarity, the same reference numbers are used for the same and similar parts in the following detailed description of the exemplary embodiments

The shoulder joint prostheses 11 shown in FIGS. 1 to 9 and 13 comprise a shaft part or shaft part 13 which can be anchored in the humerus bone of a patient, with shaft shaft 15 and shaft head 17. An articulation recess 19 is formed in the shaft head 17. A neck part 21 is articulated on the shaft part 13. This has an articulation head 25 resting in the articulation trough 19 and a neck extension 27 thereon. A calotte 29 is placed or can be placed on the neck extension 27, which interacts with an artificial glenoid 12, as shown in FIG. 1, or with a natural glenoid.

A neck axis 33 is defined by the direction of the neck extension 27. In a central position of the neck part 21, the neck axis 33 coincides with the axis of the articulation trough 19. This direction of the neck axis 31 must be set individually for each patient. Around the neck axis 33 with respect to inclination and ante or retroversion, e.g. To be able to align perpendicularly to the cut surface on the patient's bone, the neck part 21 is mounted in the articulated depression 19 in the manner of a ball joint. The neck axis can thus be deflected from the central position by an angle of approximately 20 degrees in any direction.

In Figure 1, a first embodiment of a shoulder joint prosthesis is shown, in which a circular edge 23 at the base of the articulation trough 19 a support for the ball of the articulation head 25 This circular edge 23 is formed by the mouth edge of a central second bore in the flat bottom of a first bore in the shaft head 17 forming the main volume of the articulation trough 19. The larger first bore has a radius corresponding to the ball radius of the articulation head 21, but can also be larger in order to achieve the insertion of the articulation head 25 into the articulation trough 19. The smaller second bore has a radius approximately corresponding to the circular edge 23. The articulation ball 25 is guided through the two circular edges 23, 37 of the smaller bore and the passage opening 35.

A passage opening 35 for the neck extension 27 is formed in the pressure disc 31. Their diameter can correspond to that of the second hole. The passage opening 35 has a circular opening edge 37, which abuts the pivot head 25. On one side, the pressure plate 31 is articulated with a hinge nose 39 in a hinge recess 41 in the shaft head 17. The hinge nose 39 and hinge recess 41 can be plugged into one another, so that the pressure plate 31 and shaft part 13 can be detached from one another. On the hinge side, a slot opening can be formed in the pressure plate 31 between two hinge lugs 39, so that the pressure plate 31 is horseshoe-shaped or C-shaped. On the side opposite the hinge nose, the pressure disk 31 is screwed to the shaft head 17 with a screw 43. This results in a three-point bracing between the two hinges 39, 41 and the screw 43.

If the circular edges 23 and 37 lie on the spherical surface of the articulation head 25 without pressure being exerted thereon, the neck part 21 can be pivoted in a ball-and-socket manner relative to the shaft head 17. To fix the pivot head 21 in the shaft head 17, the screw 43 is tightened. The two circular edges 23, 37 are thus moved towards one another. The circular edges 23, 37 are pressed into the spherical surface of the pivot head and plastically deform it. A very rigid connection between the shaft part 13 which can be anchored in the bone and the neck part 21 is thereby achieved.

FIG. 2 shows a second exemplary embodiment of a shoulder joint prosthesis 11. The articulation head has a spherical surface area 45 and three pointed bodies 47. The tips 49 of the pointed bodies 47 are at the same distance from the center of the sphere as the spherical surface. The tips 49 are directed against the base of the articulation trough 19. In the swivel range of the tips 49, the articulation trough 19 has a hollow spherical surface 50 with the same radius as the spherical surface of the articulation head 21. The tips 49 rest on this hollow spherical surface. The hollow spherical surface 50 is formed in the base of a cylindrical articulation trough 19. A large circle of the spherical surface of the articulation head 21 lies against the cylindrical outer surface of the articulation trough 19.

A neck extension 27 extends through a passage opening 35 in a pressure disc 31. A head cap selected from a set of head caps is attached to it. The pressure disc 31 is articulated on one side with an axis 51 on the shaft head 17 and can be pivoted about the axis 51 relative to the latter. The pressure plate 31 is C-shaped and points with the C opening 52 away from the axis 51. This makes it possible, when the pressure disc 31 is open, to first insert the articulation head 256 into the articulation trough 19 and then to fold the pressure disc back. The pressure plate 31 can be screwed to the shaft head 17 with one screw in each of the two C-legs (only the axis of the screw is shown). As in the first exemplary embodiment, the passage opening 35 here has an opening edge 37 which is directed toward the coupling head 25 located in the coupling trough 19. With this opening edge 37, when the screw 43 is tightened, the articulation head 25 is pressed against the base of the articulation trough 19. The tips 49 of the pointed bodies 47 dig into the hollow spherical surface 50 of the articulated depression 19. Depending on the pressure conditions and the materials selected, the opening edge 37 also digs into the spherical surface of the pivot head.

In the third exemplary embodiment shown in FIG. 3, the pressed part is formed by a union nut 53. This can be screwed into a thread in the edge of the articulation depression 19 in the articulation depression 19. Analogously to the union nut in the exemplary embodiments according to FIGS. 6 and 7, it can also encompass the edge of the articulation trough 19. Here, however, the union nut also lies practically along a large circle on the spherical pivot head 25 and thus forms a lateral guide for the latter. This guidance is not absolutely necessary since the guidance of the articulation head 25 has already been achieved by the two circular edges 23 and 37. The union nut grips in the same way Pressure plate 31 of the first two exemplary embodiments with the opening edge 37 of the passage opening 35 for the neck extension 27 on the pivot head 25.

The cylindrically stepped articulation trough 19 has a first radius with the thread. A smaller second radius almost has the radius of the articulation head 25. The mouth edge of this second hollow cylinder with the second radius forms a first circular edge 55. The articulation head is pressed into this second hollow cylinder when it is pressed in, a clamping fit being established between the articulation head 25 and the first circular edge 55. A second circular edge 23 with a smaller radius than the first and a body tip 57 on the axis 33 of the cylinder bore at the base of the articulation depression 19 lie approximately on a spherical surface with the same radius as the ball of the articulation head 25. When the articulation head 25 is pressed into the articulation depression 19 these notch into the surface of the articulation head.

FIG. 3 also shows a double eccentric for precisely aligning the spherical cap 29 with the contour of the cut surface on the bone. The double eccentric is composed of an eccentric ring 59 with the axis 61 that can be plugged onto the neck extension 27, and an eccentric to the calotte axis 63 in the spherical cap 29 Recess 65 for receiving the eccentric ring 59. Between the neck extension 29 and eccentric ring 59, or between the latter and the recess 65, a clamp fit is provided. The separation of neck part 21 and eccentric ring 59 is necessary because the eccentric ring 59 does not fit through the passage opening 37. If the neck extension 27 can be inserted into the articulation head 25, the eccentric ring 59 can also be produced in one piece with the neck extension 27.

Since the invention is independent of the shape of the shaft part or shaft part 13, only the shaft head 17 with the neck part 21 and press part, in some cases shown in FIGS. With. z.T. without eccentric and head cap 29 shown.

FIG. 4 shows a fourth exemplary embodiment with an articulation depression 19 in the shaft head 17 with an approximately hemispherical articulation surface 67, a union nut 53 with a concave, approximately hemispherical articulation surface 69 and a neck part 21 with a cylindrical articulation head 25. The cylindrical articulation head 25 has two circular edges 71, 73, of which one with the Articulation surface 67 of the articulation trough 19 and the other cooperates with the articulation surface 69 of the union nut 53. The circular edges 71, 73 lie on a virtual spherical surface with approximately the same radius as the spherical surfaces 67, 69 of the coupling trough 19 and union screw 53. To adjust the spherical radius of the virtual spherical surface, it is sufficient to change the length of the pivot head 25. The radius of the virtual sphere is advantageously somewhat larger than the radius of the hollow sphere surfaces of the two articulation surfaces 67, 69. A sufficient accuracy of the agreement of the two spherical radii is easy to achieve, since the articulation surfaces 67, 69 and the circular edges 71, 73 are plastically deformable.

A fifth exemplary embodiment is shown in FIG. In this case, the pressure plate 31 is not a union nut with a thread, but holds with a clamp fit in the shaft head 17. It has a hollow spherical articulation surface 69 which interacts with an interrupted circular edge 73 on a partially cylindrical articulation head 25. The circular edge 73 is broken up by incisions in the articulation head 25 to form a series of body tips 47, the tips 49 of which burrow into the articulation surface 69 when the articulation disk 31 is tied into the shaft head 17. The articulation trough 19 has two circular edges 23, 23 'which cooperate with a spherical surface 75 on the articulation head 25. In this exemplary embodiment, too, it is relatively easy to match the radii of the spherical surface 75 and the circular edge 73 on the articulation head 25 with the radii of the virtual spherical surface on which the circular edges 23, 23 'lie and the articulation surface 69 on the pressure plate 31, since the desired deformation of the contact areas permits greater tolerances than a compression of two congruent articulation surfaces. The jamming between the shaft part 13 and the pressure disc 31 can be achieved directly via a cone. However, it is better to clamp the pressure disc 31 as shown via a wedge clamp with a e.g. C-shaped wedge 76 reaching around the pressure plate

The sixth exemplary embodiment shown in FIG. 6 has a conical base 77 of the articulation depression 19 and a spherical articulation head 25 of the neck part 21. The lateral surface of the base 77 has incisions 79 in the direction of the lateral lines through the cone tip. This results in 79 edges 81 transversely between the incisions a direction of rotation about the axis 33. The pressure disk 31 is fastened to the shaft head 17 with a union nut 53. The neck part 21 is equipped in one piece with an eccentric 83. The pressure plate 31 is C-shaped. The C-opening has a width which allows the neck area 85 between the articulation head 25 and the eccentric 83 of the neck part 21 to be inserted through this C-opening into the passage opening 37 of the pressure disc 31. The union nut 53 is either also C-shaped or has an opening width that allows the union nut 53 to be pushed down over the eccentric 83 or up onto the neck part 21 via the articulation head 25. In the latter case, the union nut must first be pushed over the articulation head 25 and then the pressure disk 31 must be inserted between the articulation head 25 and union nut 53. The link plate 31 can be rotated in this example relative to the union nut 53. This has the advantage that hardly any torque is transmitted to the neck part 21 when the union nut 53 is tightened. When the union nut 53 is tightened, the opening edge 37 is not rotated relative to the articulation head 25, but rather only pressed against it. In the non-tightened state, the neck part 21 can be rotated about the neck axis 33. As a result, the eccentric 83 can be brought into the desired position.

FIG. 7 shows, based on a seventh exemplary embodiment, a very simple variant of the pressure plate and a further possibility of combining cylindrical and spherical bodies and openings in order to achieve an already repeatedly executed spherical gel-like connection between the coupling trough and the coupling head or between the shaft head 17 and the neck part 21. In this example the articulation trough has a hemispherical base 67, which cooperates with a circular edge 23 of a cylindrical articulation head 25, but the articulation head 31 is of spherical shape so that the circular opening edge 37 of the pressure washer 31 rests on the articulation head equally in every pivoting position thereof. The articulation disk 31 can be screwed onto the shaft head 17 with two screws 43.

FIG. 8 also illustrates that the invention can also do without a pressure disk 31. The neck part 21 is cylindrical in this eighth exemplary embodiment and, thanks to a gradation of the articulation head 25, has two circular edges 23, 23 'on a virtual spherical surface. These circular edges 23, 23 'work together with the Hollow ball surface of the articulation recess 19. The neck part 21 is now hollow and a screw 87 is seated in this cavity 89 in such a way that its threaded section exits through an opening in the neck part and can be screwed into the base of the articulation recess. A circular edge 91 is formed on the frustoconical screw head cooperates with a hollow spherical surface at the bottom of the cavity 89. The neck part 21 is formed in one piece with the eccentric 83. In the tightened state of the screw 87, the edges 91, 23, 23 'are pressed into the spherical surfaces and thereby reliably prevent the neck part 21 from pivoting relative to the shaft head 17. Then the spherical centers of the various spherical surfaces advantageously advantageously coincide. Smaller deviations from an exact match of the spherical centers are compensated for by the deformations.

The exemplary embodiments can also be modified such that the articulation trough is formed in the neck part and the articulation head in the shaft head. The neck extension does not have to be formed in one piece with the articulation head, but can be provided as a stem which can be fixed in the articulation head. The design of the press part is largely independent of the design of the articulation surfaces between the articulation trough and articulation head, so that the most varied combinations are possible under the design variations shown and mentioned.

It should also be mentioned that, for example, the articulation head 25 need not be a full body. For example, as shown in FIGS. 9 to 11, it can be composed of individual parts. FIGS. 9 and 10 show the views of two plate-shaped parts 93 and 95 which can be plugged together. Together, the parts 93, 95 result in a neck part 21 which can be used instead of the neck part 21 in FIG. The parts 93.95 are easy to manufacture. For example, they can be cut from a plate with a laser or cast. The edge surface 97 need not be a spherical surface. By pressing into the articulation recess, the edges 99 are deformed in such a way that both a large-area support and a very good toothing between the shaft head 17 and the neck part 21 is achieved. The part 93 in FIG. 9 is with the slot 101 via the slot 103 on the part 95 in FIG. 10 can be pushed onto this part 95 so that all edges 99 lie on a common spherical surface. A groove is formed in the neck extension 27 in both parts 93.95, into which a screw 105 can be screwed.

The neck extension 27 from both parts 93, 93 forms a cross with a central, square recess. The eccentric ring 59 can now be placed on this cross. Thanks to the cross shape of the neck extension 27 and a corresponding recess in the eccentric ring, rotation of the eccentric ring 59 relative to the neck part 21 is impossible. To fix the eccentric ring 59 on the neck extension 27 and the two parts 93.95 to one another, the screw 105 can now be screwed in, which causes jamming between the parts 93.95 on the one hand and the eccentric ring 59 on the other. FIG. 11 shows the assembled neck part 21 with eccentric ring 59 in a top view. In this view it can be seen how the edge surfaces 97 of the two parts are formed orthogonally to the plate plane.

FIG. 12 shows a tenth embodiment in which the neck part 21 is composed of two parts 93.95. The neck part 21 corresponds exactly to the neck part 21 shown in FIGS. 9 to 11 except for the shape of the articulation head 25 cylindrical hinge 19 equipped in which a body edge 23 is formed, on which the edges 99 of the neck portion 21 abut. The neck part 21 is pressed with a pressure disk 31 against the base of the articulation trough 19. The force with which the pressure disk 31 is pressed against the shaft 13 is transmitted to the shaft 13 by a clamping bracket 107. The clamping bracket 107 lies on the outside of the pressure disc 31 and engages behind an undercut 109 in the shaft head 17. It is made of a resilient material, so that a relatively large force is exerted on the pressure plate. The clamping bracket 107 can also form the pressure disc 31 directly.

Claims (17)

1. A joint prosthesis (11), with

   - an artificial joint socket (12) for anchoring in a first bone, or for an articulating co-operation with a natural joint socket in a first bone,

   - a shaft piece (13) for anchoring in a second bone,

   - a joint cavity (19) in the shaft piece (13),

   - a collar piece (21) which defines a collar axis and comprises a joint head (25), which joint head (25) is disposed in the joint cavity (19),

   - articulation surfaces so co-operating in the joint cavity (19) and at the joint head (25) that the collar piece (21) is articulated on the shaft piece in the manner of a ball joint,

   - at least one pressure piece (31, 53, 87) for pressing the joint head (25) into the joint cavity (19) and

   - means (53, 43) for connecting the pressure piece (31, 53, 87) and the shaft piece (13), and

   - a head cap (29) disposed on the collar piece (21),

   characterized in that

   - a first one of the two co-operating articulation surfaces (e.g. 23, 23', 49, 50, 57, 67, 71, 75, 81, 99) has at least one edge and/or point and the second articulation surface lies on a virtual spherical surface so that only one or more punctiform and/or linear contact zones are present between the first articulation surface and the second articulation surface and

   - in that the articulation surfaces are so constructed in respect of material that under the action of the pressure forces occurring during pressing into contact at least the second articulation surface (for example 23, 23', 49, 50, 57, 67, 71, 75, 81, 99) is plastically deformable by the edge and/or point of the first articulation surface.
2. A joint prosthesis according to claim 1, characterized in that the second articulation surface is formed by a smooth or rough surface zone (for example, 50, 67, 75).
3. A joint prosthesis according to claim 1 or 2, characterized in that the edges (e.g. 81) are situated transversely of a direction of rotation of the collar piece (21) about its collar axis (33).
4. A joint prosthesis according to any one of claims 1 to 3, characterized in that the spherical surface zone has grooves.
5. A joint prosthesis according to claim 4, characterized in that the grooves are situated transversely of a direction of rotation of the collar piece (21) about its collar axis (33).
6. A joint prosthesis according to any one of claims 1 to 5, characterized in that at least one continuous or interrupted linear contact exists between the joint head (25) and the pressure piece (31, 53, 87).
7. A joint prosthesis according to any one of claims 1 to 6, characterized in that the pressure piece (31, 53, 87) and the shaft piece (13) are adapted to be screwed together.
8. A joint prosthesis according to any one of claims 1 to 7, characterized in that the pressure piece comprises a pressure disc (31, 53) with a passage opening (35) for the collar piece (21).
9. A joint prosthesis according to claim 8, characterized in that the pressure disc (31) is annular.
10. A joint prosthesis according to claim 9, characterized in that the pressure disc (31) is C-shaped.
11. A joint prosthesis according to any one of claims 7 to 10, characterized in that the pressure piece is a cap nut (53) or is fixable by a cap nut (53).
12. A joint prosthesis according to any one of claims 7 to 11, characterized in that the pressure disc (31) is rotatable relatively to the shaft piece (13) about an axis through the passage opening (35).
13. A joint prosthesis according to claim 11, at least in conjunction with claim 12, characterized in that the cap nut (53) is adapted to be connected to the shaft piece (13) by a bayonet fastener.
14. A joint prosthesis according to any one of claims 1 to 11, characterized in that the pressure piece (31, 53, 87) is non-rotatable relatively to the shaft piece (13) with respect to an axis through the passage opening (35).
15. A joint prosthesis according to any one of claims 7 to 10, characterized in that the pressure disc (31) is adapted to be connected to the shaft piece (13) by resilient clamping means (107).
16. A joint prosthesis according to any one of claims 1 to 8, optionally in conjunction with claim 11 or 12, characterized in that the pressure disc (31) is fixed on the shaft piece (13) so as to be pivotable about an axis transversely of the collar axis (33).
17. A joint prosthesis according to any one of claims 1 to 10, optionally in conjunction with any one of claims 15 to 17, characterized in that the pressure disc (31) is adapted to be clamped fast on the shaft piece (13) by a clamping connection, for example a wedge clamping.